Case Report on T-LGL and mRNA vaccine adverse event

We describe the occurrence of pure white cell aplasia within days following the first dose of a mRNA-1273 vaccination against COVID-19. The patient was subsequently diagnosed with a STAT3 wild-type T-cell large granular lymphocytic leukemia (T-LGL) and neutropenia was successfully treated with IVIG, glucocorticoids, and G-CSF. The mRNA-1273 vaccine, but not the Ad26.COV2.S vector vaccine triggered strong IL-6/STAT3 activation in vitro, resulting in excessive T-cell activation and neutrophil degranulation in the patient but not in controls. Second dose COVID-19 immunization was safely completed with a single dose of the Ad26.COV2.S vector vaccine without reoccurrence of neutropenia. The T-LGL clone remained stable during the follow-up of more than 12 months without ongoing therapy. Switching the immunization platform may be a reasonable approach in subjects with rare associated hematologic side effects do to excess STAT3 mediated stimulation following mRNA vaccination.